Tone arm mounting



Jan. 6, 1948. I R. M. CAIN 2,434,033

TONE ARM MOUNTING Filed May 23, 1945 s Sheets-Sheet 1 INVENTOR.

Jan. 6, 1948. RM. CAIN TONE ARM uoumme Filed May 25, 1945 5 Sheets-Sheet 2 w Q J 2,. g 55:55 I n q. .r n. r... C L4. Q mq 7 m rmw m 'INVENTOR.

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Jan. 6, 1948. R. M.CA]N 7 2,434,033

Toma: ARM uoumme. Filed May 23, 1945 s Sheets-Sheet s INVENTOR. (m 11 BY "T "i i able Qunti-ng which Will r sult in the abilitylof Patented Jan. 6, 1948 Cain, Charlotte, Mich., assignor to Wilo Corporation. Cha lotte Mich a @01- poratioh of Michigan Application May 23, 1945, Serial No. 595,293

This invention relates to mechanisms for carrying the pick-up or playback arm of a phonograph.

In order for the pick-up arm to follow the groove of a conventional disc record, it is n essary that the arm swing first about a vertical axisso that it mayv follow the spiralling of the grooves; and, second, it is necessary that it also rotate about a horizontal axis sothat the needle may follow up and down variations in the record, and so that the pick-up arm may be raised for removal or insertion of the record.

In many phonograph designs incorporating pivots or shafts as the horizontal axis, there is usually a certain amount of friction opposing the rotation. This friction adds itself to the weight of the pick-up arm on the up..di rect ion and subtracts itself from the weight of the pickup arm on the down direction. It can be seen then that the actual change in needle pressure, due to this axial friction, is substantially twice the increment of friction.

While this change in needle pressure might represent a relatively small percentage of the total in phonographs having needle pressures of several ounces or more, it represents a substantial percentage of the total in pick-ups of the light weight class.

In the playing of most phonograph records there is present a certain amount of scratch noise. The amount of this scratch is dependent on several factors such as the initial quality of the record, the extent to which ithas previously been played, the response of the pick-up device and associated amplifying circuits, the reproducing stylus and, to a large extent, the associated weight.

When playing phonograph records of .the conventional disc type on record playing machines of existing design, the up and down variations of record surface result in a varying scratch level due to the variation in needle weight. The variation in scratch level actually makes the noise more noticeable and therefore more objectionable tnan it would if it were substantially steady.

One means of maintaining constant needle pressure in a phonograph pick-up arm and consequently constant scratch level would be to play .only the fiattest of record surfaces on an exactly true turntable thereby maintaining constant neede elevation. This would be commercially unfeasible.

It is therefore an object of this invention to provide a phonograph pick-up .arm and a suit- 3 Claims. (C1. 274123) the rep odu in needle to follow u hi dow variations in thereconi and et. ma nta sii ciently constant ne dle-pressure s that a hi order o n se cn tano i ob ained,

.nh noeraphs us e i ker arm a 9.

r ae ia ask-u devise i is de irab tha prope n dl essure h emple ed- T i Pre sure should be s lent i9 cau e h nesdle i to bea against bat wa s o the groove at a times. ,Greater pressure than an amount necessary to accomplish this results in excessive wear .onboth the needle and the record. Insuflicient pressure allows the needle to climb the walls of t e roove and esu t in a i tort n of the reproduct on. phonographs having a certain amount of friction opposing the vertical rotation of the pickup arm, it is necessary that the static needle pressure be .v n k h greater than the amount necessary for proper traclging'so that when the arm i following a downward variation of the record surface, the loss in weight due to the axial ct on wil still l av u iq nt fo pr r t acking. As "has already been shown, the needle weight rbecomes still greater when the arm is following an upward variation in the record and the axial friction adds itself to the already overweightedarm. I

It is another obiect, therefore, of this invention to provide a phonograph arm and a suitable mounting in which the horizontal axial friction opposing the vertical rotation of the arm is negligible.

It is a further object of this invention to combine with the mechanism which facilitates vertical movement of the pick-up arm means for adjusting the needle pressure.

It is a further object of this invention to proportion the dimensions and divisions of stops in such a .mannerthat two objectional accidents cannot occur, namely, that it .will be impossible for the needle holder to drag on the record in the absence .of a needle and that it will be impossible for the needle :to drag on the turntable theabsence o a record.

It is another object of this invention to so arrange the stops and needle pressure control means (such as a tension spring) that the adjustment of the tension spring remains substantially constant and the needle pressure control m s s not un ul relaxe when the pi k-up arm is raised.

The foreg n and-man ot r o j ts of my invention w b m ap n th ql owing de tiniivn nddrawinssinwh qh Figure 1 is a schematic diagram of the essential mechanism for accomplishing the purposes of this invention.

Figure 2 is a plan view of a practical embodiment of the invention.

Figure 3 is an elevation in partial section of the mechanism of Figure 1 taken on line 33 of Figure 2.

Figure 4 is a rear view in section of Figure 3.

Figure 5 is a top sectional View through the plane indicated in Figure 3 by the numbers 5-5.

Figure 6 is a reproduction of part of Figure 3' with the playback arm in a partly elevated position. I

Figure '7 is a reproduction of Figure 6with the playback arm elevated to a vertical position.

Referring to Figure 1, the pick-up arm supporting assembly a carries the play-back arm I and is mounted on supporting assembly b. The playback arm I, needle I2 and its rearwardly directed extension-carrying pin 6 are all supported on a knife edge bearing I0 resting, in turn, on assembly b consisting of a fulcrum II carried on a support 2 which is pivoted on pin 5.

As was mentioned previously, it is necessary for a pick-up arm to rotate first of all in a horizontal plane around a vertical axis. By means of a vertical spindle secured to the support of pin 5, a frame of reference rotatable about a vertical axis is established. The plane of the drawing of Figure 1 is presumed to be attached to this frame of reference rotating around the vertical axis. More specifically, assembly 1) is pinned to this frame of reference by means of pin 5 which forms a horizontal axis around which assembly 1) may rotate. Stop 3 is also attached to this frame of reference.

In Figure 1, W represents the weight at the center of gravity of the pick-up arm. The weights of other members are functionally negligible. In Figure 1, the mechanism is shown in an intermediary position in which there could not be an equilibrium under the action of the weight W alone. In this position, assembly a is still free to rotate about fulcrum II, and assembly b is still free to rotate about'pin 5. Under the action of Weight W, assembl b would rotate around pin 5 until member 2 struck stop 3, after which assembly I) would become relatively rigid with the frame of reference. Thereafter, assembly a would rotate around fulcrum II until member 9 struck stop 'I. In this position, the force exerted by stop I and stop 3 would bring the mechanism to equilibrium, in the absence of any needle forces exerted at I 2 or in the absence of a tension spring such as spring 4.

In this invention, the positioning of the stops seen that the force on the needle required to raise assembly a would be nearly equal to the Weight of the entire pick-up. If, however, the first of these conditions obtains, then it is seen that the force required at the needle would be determined by the tension of spring 4 as well as by the weight of the pick-up armand it is seen that the greater the tension of spring 4, the less force is required at I2.

Since the desirable needle pressure is always considerably less than the weight of the pick-up arm, it is one of the purposes of this invention to adjust the tension of spring 4 so that a relatively small force exerted at I2 will lift the mechnism out of the equilibrium positive by the first mentioned possibility-namely, that assembly a rotate first about fulcrum II, While assembly b remains relatively rigid to the frame of reference 'by resting on stop 3.

In this invention the dimensions would be so and other dimensions may be so arranged that this condition would obtain if no needle Were in the pick-up arm or if no record were on the turntable. This would make it impossible for the needle holder to drag on the record or for the needle to drag on the turntable. If, however, a record were on the turntable and a needle were in the holder, the needle would strike the record before this position is attained.

As the playback arm is lifted by a force applied at I2 to move the mechanism out of the previously described position of equilibrium, it can be seen that not only is it possible for assembly a to begin to rotate around fulcrum I I, but that it isalso possible for the relatively rigidcombination of assemblies a and b to begin to rotate around pin 5. If the second of these positions obtains,it is a record on the'turntable and a needle in the holder, member 9 would lie between stops 1 and 8 touching neither even for any possible vertical movement of one due to irregularities in the rec- 0rd or turntable.

In a practical embodiment of the invention, as will be shown later, the tension of spring 4 is adjustable so that various desired needle pressures may be obtained.

Also, it will be seen that the tension on spring 4 will be varied in operation only by the degree of movement of the playback arm between stops 1 and 8; and after member 9 has struck stop 8, tension of spring 4 will cease to relax. Accordingly, spring 4 may, if desired, simply be hooked over pins 6 and 5 and will not be accidentally released.

If now it is desired to change a record or to move the pick-up arm out of the way for any other purpose, such as Would be necessary if the pick-up arm were used as a playback arm on a record cutting machine (having other elements which must cooperate with the turntable to cut a record), one lifts member I by the application of additional manual forces at I2. When this is done, assembly a rotates around fulcrum II until member 9 strikes stop 8, after which members a and I) become relatively rigid and rotate around pin 5. The extent of this rotation is limited only by other obstructions.

In a practical embodiment of the invention, elements would be so arranged that rotation around pin 5 is possible until the center of gravity represented in Figure 1 by W has at least passed to the right of pin 5, after which the pick-up arm would strike some obstruction. The weight W would then hold the arm in the elevated position.

From Figure 1, it is seen that it is possible to remove knife edge I II from V-groove I I entirely by the application of proper forces. In a practical embodiment of the invention, as will be shown later, stops may be arranged so that this cannot happen inadvertently.

Referring now to Figures 2 and 3, the phonograph base plate I9 carries the rotatable turntable I8 in any suitable manner and the vertical journal I3 of the pick-up arm assembly which journal is bolted to the base I9 by means of nut I! and washer I6. Through this journal I3 runs a spindle I5 to which is rigidly attached member R. The upper part of journal I3 is reduced in diameter at I4 and the top face of this reduced portion 'ofjournal I3 cooperates with the underrotation in ahorizontal plane of member R and consequently of the .pick-up arm.

In this practical embodiment of the invention, member :R is the frame .of reference to which the schematic diagram .of .Figure 1 was referred- Member R comprises av single piece of sheet metal,

bent along three lines to form a horizontal and three vertical parts. The horizontal part which attachesto spindle .I.5 carries the vertical parts which form a fork-shaped yoke. The pin is carried in any suitable manner between the sides of the yoke. Pin 5 carries member B. Member B consists of a piece of sheet metal bent into a channel, the lower extremity of the sides of this channel being drilled to cooperate with pin 5. Member 13 therefore is rotatable about pin 5. The upper extremities of the sides of member B have V-slots II on which bear a knife edge I9 which is part of member 9. Member 9 consists of a piece of sheet metal with a single bend forming an inverted L.

The vertical side of member 9 is cut away, as shown most clearly in Figure 4., to form the knife edges II] and to extend downward to extremity 9a, whose operational function was described in Figure 1. Member 9 is spot welded or otherwise permanently attached to main pick-up arm I, which has the form of a channel member closed on both ends.

Pick-up arm I carries at one extremity needle I2 and an electrical pick-up mechanism not shown. The other extremity of member I is drilled to pass machine screw I9. Machine screw I9 passes also through a hole in member 9. The inner end of screw I9 is enlarged so that it may not be removed from the position shown in Figure 3; it is, however, free to rotate, the holes in members 9 and I serving as bearings. Screw I9 carries a threaded tab 6 perforated at its end to engage one end of spring 4, the other end of spring 4 being hooked around pin 5.

The numbers shown in Figures 2 to 7 inclusive represent members which are functionally identical with the numbers used in Figure 1.

In Figure 3, member 13 is shown rotated in a counterclockwise direction around pin 5 into engagement with the upper part of member R. The point of contact on R to member B in this position serves as the stop 3.

In Figure 3, it is also seen that the tongue 9a of member 9 extends between pin 5 and the bottom of member B. In this position, therefore, members R and B are rigid with respect to each other and pick-up arm I is free to rotate around fulcrum II in response to needle pressure on I2. The degree of this needle pressure, which is determined by the effectiveness of spring 4, is adjustable by a rotation of screw I9 which advances or retards tab 6 with which spring 4 is engaged.

If, however, no needle is present or if no record is present, the tongue of member 9 will strike pin 5 or the end around pin 5, one of these thereby performing the function of stop I of Figure l, and will check the counterclockwise rotation of member I before damage is done to the record by an empty needle holder or to the turntable by the needle.

If it is now desired to put the pick-up arm out of the way and if pick-up arm I is for this purpose rotated in a clockwise direction, rotation will take place first of all around fulcrum I I until the of spring 4 which is wrapped .pos'ition ;shown in Figure :6 isiattained. :At this instant, the tongue 9 will strike member .13 zatf'the --point :8,.which :serveszas the .stop .shownlinifiligme .1. If the clockwise rotation of pick-up=arm I :is

. continued, .assembly'a' and memberIB' will become relatively rigid :and rotate around .pin :5. This rotation .can be continued until 1pick up :arm' TI is in the :vertical position shown in Figure i7. By

this time, the center of gravit is obviously to the right of pin 5 and clockwise rotation would continue due .to ithe weight alone, unless checked by a stop which would of course be provided in the most convenient manner.

.Ill:iS .p0SSib1e to make the V notches ;II sufficiently deep so that the sides thereof, bearing against the sides of knife edge member III, will furnish the stops 1 and B.

To prevent the accidental removal of the knife edge I0 from V-groove II, member B is drilled and threaded to receive screw 2I, as shown in Figures 3 and 5. Member 9 is drilled with a large clearance hole 22 to pass screw 2I. The clearance hole in member 9 is so large that it does not touch screw 2| under all normal conditions; however, it is now impossible to remove assembly A from member 1) without first removing screw 2| with a screw driver.

Figures 2 to 7 inclusive represent one practical embodiment of the mechanism of Figure 1 which accomplishes the purposes of the invention.

In the foregoing, I have described my invention only in connection with a specific effective embodiment thereof. Since my invention is capable of many variations and modifications which will be obvious to those skilled in the art, I prefer to be bound not by the specific disclosures herein but only by the appended claims.

I claim:

1. A phonograph tone arm mounting comprising a member rotatable in a horizontal plane, a tone arm support carried by said member; said support being rotatable with respect to said member in a vertical plane; a tone arm mounted on said support and rotatable with respect thereto in a vertical plane; means for limiting the rotation of said tone arm with respect to said support to a predetermined arc, said tone arm projecting substantially beyond its rotatable mounting on its support on one side of said mounting and projecting to a lesser degree on the other side of said mounting; and means for counterbalancing at least a portion of the weight of said tone arm on said first mentioned side, said last mentioned means comprising a, spring connected at one end to said other side of the tone arm and at the other end to the pivot of said support.

2. A phonograph tone arm mounting comprising a member rotatable in a horizontal plane, a

tone arm support carried by said member; said support being rotatable with respect to said member in a vertical plane; a tone arm mounted on said support and rotatable with respect thereto in a vertical plane; and means for limiting the rotation of said tone arm with respect to said support to a predetermined arc, said means comprising a dependent member connected to said tone arm; a pair of stop members on said support; said extension extending between said stop members. v

3. A phonograph tone arm mounting comprising a member rotatable in a horizontal plane, a tone arm support carried by said member; said support being rotatable with respect to said member in a vertical plane; a tone arm mounted on said support and rotatable with respect thereto 7 in a 'vertical plane; and means for limiting the rotation ofsaid tone arm with respect to said support to a predetermined arc, said'means comprising a V-shaped notch at the upper end of said support; and a vertical knife edge extension of said tone arm engaging said notch, and an additional dependent member connected 'to said tone arm; a pair of stop members on said support; said extension extending between said stop members.

ROBERT M. CAIN.

REFERENCES CITED The following references are of record in the file of this patent:

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